NEWARK, Calif., July 1, 2013 (GLOBE NEWSWIRE) -- StemCells, Inc. (Nasdaq:STEM) today announced its addition to the Russell Microcap Index following Russell Investments' reconstitution of its comprehensive set of U.S. and global equity indexes. The Russell Microcap Index measures the performance of the microcap segment of the U.S. equity market. Microcap stocks make up less than 3 percent of the U.S. equity market (by market cap) and consist of the smallest 1,000 securities in the small-cap Russell 2000® Index, plus the next smallest eligible securities by market cap.